The measurement data from NDT/NDI devices used for the routine monitoring of structural integrity must be of sufficient accuracy to allow a valid assessment to be made of the conditions of the structure under test. Examples of such structures are pipes and vessels widely used in the petrochemical and other industries. Examples of measurement data are pipe wall thickness and other geometric conditions, including, but not limited to, the presence of irregular surfaces (e.g. corrosion, oxide, etc.) and flaws (e.g. porosity, cracks, etc.).
Often, the decision to perform or not perform maintenance on a structure is made based on the assessment of the measurement data. Therefore, the measurement accuracy will have a direct impact on the decision. The consequence of inaccurate measurement data that underestimates an unfavorable condition of a structure can result in failures occurring before maintenance is performed. Conversely, inaccurate measurement data that overestimates an unfavorable condition of a structure can result in performing expensive and unnecessary maintenance.
One of the most common NDT/NDI devices used for assessing structural integrity is an eddy current (herein after as “EC”) instrument for examining conductivity of conductive materials. In a typical eddy current inspection operation, an eddy current array probe, comprising a plurality of coils, is placed adjacent to the surface of a material under inspection. At the start of an inspection operation, an NDI instrument coupled to the eddy current probe energizes one or more coils. This, in turn, induces a current in the material under inspection. One or more coils within the probe array then sense this induced current and provide a measurement signal to the NDI instrument. By measuring the current induced in a material under inspection, the impedance or conductivity of said material can be calculated. Further, by tracking the impedance of a material under inspection as the probe is moved along the surface of said material flaws and defects within said material can be found and analyzed for anomaly reading of the impedance or conductivity.
The specific challenge herein dealt with is that the instrument needs to be calibrated for all different types of EC probes designed to work with instrument.
One conventional solution for EC probe calibration employs pre-defined static data tables to compensate for the time distortion; however, this solution has the drawback of not accounting for actual conditions of the probe in use since it only calibrates for one type of the probe. However, all probes of the same type can differ due to various reasons including probe wear and manufacturing variances in probe population. The conventional method also does not account for any drifts caused by change in environment, such as temperature.
The conventional method of determining conductivity and thickness is of standard in the field of conductivity measurements using eddy current. One can refer to ASTM E1004—09 Standard Test Method for Determining Electrical Conductivity Using the Electromagnetic (Eddy-Current) Method, Active Standard ASTM E1004 | Developed by Subcommittee: E07.07, Book of Standards Volume: 03.03.
Current empirical calibration data table using a pre-determined data table, use empirical methods of deriving data to generate the Table. The predetermined Table is generated by using conductivity measurement methods on a batch of typical eddy current probes of one model. It is then used for hundreds of the probes of the same model for many years. The existing calibration table is herein referred to as the “Empirical Table”. Once can refer to one of these existing standard, or particularly, AC Conductivity Standards for the Calibration of Eddy-Current Conductivity Meters”, by A E Drake and A C Lynch, 1987 J. Phys. E: Sci. Instrum. 20 137. doi:10.1088/0022-3735/20/2/003.
Accordingly, a solution that overcomes the drawbacks described above and results in advantages highly valued by potentially affected industrial and public infrastructure concerns, needs to:
a. improve measurement accuracy by using probe-specific reference tables;
b. allow support and usage of third party, out-of-design-spec probes; and
c. allow customer additions of future new probes.